JP2006164860A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery in which low temperature characteristics can be improved without losing cycle properties of the lithium secondary battery. <P>SOLUTION: The lithium secondary battery has in a container a positive electrode capable of storing and releasing lithium ions, a negative electrode capable of storing and releasing lithium ions, a separator arranged between the positive electrode and the negative electrode, and an organic electrolytic solution. The organic electrolytic solution contains a cyclic carbonate solvent shown in a formula 1, an aliphatic carbonate solvent shown in a formula 2, and an aliphatic ester solvent shown in a formula 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel lithium secondary battery having high input / output performance and suitable for an electric hybrid vehicle or the like.

  From the viewpoints of environmental protection and energy saving, hybrid electric vehicles using both an engine and a motor as a power source have been developed and commercialized. In the future, fuel cell hybrid vehicles that use fuel cells instead of engines are also actively developed. A secondary battery capable of repeatedly charging and discharging electricity as an energy source of this electric hybrid vehicle is an essential technology.

  Among them, the lithium secondary battery has a high operating voltage and is easy to obtain a high output, so it is a useful battery, and will become increasingly important as a power source for hybrid vehicles in the future. The electrolyte solution for a lithium secondary battery requires high withstand voltage characteristics, and an organic electrolyte solution using an organic solvent as a solvent is used. However, the organic solvent has poor lithium salt solubility and has a large temperature dependency of electrical conductivity. For this reason, there arises a problem that the operating characteristics at low temperatures are greatly deteriorated with respect to the operating characteristics at room temperature.

  Currently, carbonate compounds are mainly used as electrolyte solvents for lithium secondary batteries because of their high voltage resistance. A cyclic carbonate solvent has high lithium salt solubility but high viscosity. On the other hand, chain carbonates have low viscosity but poor lithium salt solubility. Therefore, in general, a cyclic carbonate and a chain carbonate are mixed and used as an electrolytic solution. As a method for improving the low-temperature characteristics, Patent Document 1 proposes using ethyl methyl carbonate having an asymmetric structure for the chain carbonate ester, but there is a limit to the improvement in characteristics due to the solubility of lithium salt. It was.

  As an improvement measure, Patent Document 2 proposes to use acetates which are solvents having a lower molecular weight, lower viscosity and lower melting point than ethyl methyl carbonate.

Japanese Patent Laid-Open No. 2-148665 Japanese Patent Laid-Open No. 9-245838

  However, acetic acid esters have a disadvantage that the resistance to reduction is inferior to that of a carbonic acid ester solvent, and when acetic acid esters are used singly or in combination, there is a problem that the rate of increase in resistance during cycling is increased. In addition, a film is formed on the electrode in order to suppress an increase in resistance during the cycle. However, when this method is used, the improvement of the low-temperature characteristics, which is the original problem, cannot be achieved.

  An object of the present invention is to provide a lithium secondary battery capable of improving the low temperature characteristics without impairing the cycle characteristics of the lithium secondary battery.

  The present invention improves the electrical conductivity at room temperature and low temperature by adjusting the solvent and additives of the electrolytic solution, and further mixes the electrode film forming material in order to suppress the resistance change during the cycle, or The main feature is that a lithium salt composed of an anion having a large molecular weight is mixed in order to reduce the electrode interface resistance at a low temperature.

That is, the present invention includes a container in which a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, an organic electrolyte, In the lithium secondary battery comprising:
Cyclic carbonate solvent represented by (Formula 1)

（式中、Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４は水素、フツ素、塩素、炭素数１〜３のアルキル基、フッ素化されたアルキル基のいずれかを表わし、Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４はそれぞれ同一でも異なっていても良い）
（式２）で表される鎖状カーボネート溶媒及び

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ represent any one of hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, and a fluorinated alkyl group, and R ₁ , R ₂ , R ₃ and R ₄ may be the same or different.
A chain carbonate solvent represented by (Formula 2) and

（式中、Ｒ_５、Ｒ_６は水素、フッ素、塩素、炭素数１〜３のアルキル基、フッ素化されたアルキル基のいずれかを表わし、Ｒ_５、Ｒ_６はそれぞれ同一でも異なっていても良い)
（式３）で表される鎖状エステル溶媒

(In the formula, R ₅ and R _{6 each} represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₅ and R ₆ may be the same or different. good)
A chain ester solvent represented by Formula 3

（式中、Ｒ_７、Ｒ_８は水素、フツ素、塩素、炭素数１〜３のアルキル基、フッ素化されたアルキル基のいずれかを表わし、Ｒ_７、Ｒ_８はそれぞれ同一でも異なっていても良い)
を含むことを特徴とする。

(In the formula, R ₇ and R ₈ represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₇ and R ₈ are the same or different, respectively. Also good)
It is characterized by including.

The organic electrolyte further comprises
A compound represented by (formula 4) and

（式中、Ｒ_９、Ｒ_１０は水素、フツ素、塩素、炭素数１〜３のアルキル基、フッ素化されたアルキル基のいずれかを表わし、Ｒ_９、Ｒ_１０はそれぞれ同一でも異なっていても良い）
（式５）で表される化合物

(Wherein R ₉ and R ₁₀ represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₉ and R ₁₀ are the same or different. Also good)
Compound represented by Formula 5

の少なくとも１種を含むことを特徴とする。

It is characterized by including at least 1 sort of.

  The electrolytic solution for carrying out the present invention includes ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), trifluoropropylene carbonate (TFPC), chloroethylene as the solvent represented by (formula 1). Carbonate (ClEC), trifluoroethylene carbonate (TFEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), etc. can be used, and in particular, EC is used from the viewpoint of film formation on the negative electrode. Is preferred. In addition, addition of a small amount of C1EC, FEC, or VEC is also involved in electrode film formation, and provides good cycle characteristics. Furthermore, since TFPC and DFEC have a film-forming ability with respect to the positive electrode, it is preferable to mix them in small amounts.

  Further, in the electrolyte solution, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), jetyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) are used as the solvent represented by (Formula 2). ), Trifluoromethyl ethyl carbonate (TFMEC), 1, 1, 1, 1 trifluoroethyl methyl carbonate (TFEMC) and the like can be used.

  DMC is a highly compatible solvent and is suitable for use by mixing with EC or the like. DEC has a lower melting point than DMC and is a suitable solvent for low temperature characteristics. EMC is more suitable for low-temperature properties because of its asymmetric molecular structure and low melting point. Since EPC and TFMEC have propylene side chains and an asymmetric molecular structure, they are suitable as adjusting solvents for low temperature characteristics. TFEMC has a large dipole moment by fluorinating a part of the molecule, is suitable for maintaining the dissociation property of the lithium salt at low temperature, and is effective in low temperature characteristics.

  Further, in the electrolytic solution, as a solvent represented by (formula 3), methyl formate (FA), ethyl formate (FE), methyl acetate (MA), ethyl acetate (EA), methyl propionate (PM), propion Ethyl acid (PE), methyl trifluoroacetate (TFMA), ethyl trifluoroacetate (TFME), or the like can be used. FA and FE are suitable for improving low-temperature characteristics because of their low molecular weight and low viscosity. MA and EA have a large molecular dipole moment and are effective in maintaining dissociation properties at low temperatures, and are suitable for improving low-temperature characteristics. Since TFMA and TFME have an appropriate molecular weight, they are effective in adjusting the solution structure at low temperature, and are suitable as an auxiliary mixed solvent for improving low temperature characteristics.

  Further, in the electrolyte solution, vinylene carbonate (VC), methyl vinylene carbonate (MVC), dimethyl vinylene carbonate (DMVC), ethyl vinylene carbonate (EVC), jetyl vinylene carbonate (EVC) can be used as the compound represented by (Formula 4). DEVC) or the like can be used. VC + has a low molecular weight and is considered to form a dense electrode film. MVC, DMVC, EVC, DEVC, and the like in which an alkyl group is substituted for VC are considered to form an electrode film having a low density in accordance with the size of the alkyl chain, and are considered to work effectively to improve low-temperature characteristics.

  Furthermore, the compound of (Formula 5) can adjust the structure and density of the electrode film by mixing with a part or plural of the compound group of (Formula 4), and is effective in improving the low temperature characteristics. A compound. It seems that this compound forms a suitable lithium ion migration path by reacting and depositing on the surface of the negative electrode carbonaceous material during the first charge.

The lithium salt used in the electrolytic solution is not particularly limited, but for inorganic lithium salts, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiI, LiCl, LiBr, etc., and for organic lithium salts, LiB [OCOCF 3] ₄ , LiB [ OCOCF ₂ CF ₃ ] ₄ , LiPF ₄ (CF ₃ ) ₂ , LiN (S 0 ₂ CF ₃ ) ₂ , LiN (S 0 ₂ CF ₂ CF ₃ ) _2, or the like can be used. In particular, LiPF ₆ frequently used in consumer batteries is a suitable material because of the stability of quality. LiB [OCOCF ₃ ] ₄ is an effective material because it has good dissociation and solubility and high conductivity at a low concentration.

The positive electrode material includes a composition formula LiMn _x M1 _y M2z0 ₂ (wherein M1 is at least one selected from Co and Ni, and M2 is at least one selected from Co, Ni, A1, B, Fe, Mg, Cr) X + y + z = 1, O.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.4, 0.05 ≦ z ≦ 0.4), LiMn ₄ Ni ₃ Co ₂ 0 ₂ , LiMn _1/3 Ni _1/3 Co _1/3 0 ₂ , LiMn ₃ Ni ₄ Co ₃ 0 ₂ , LiMn _3.5 Ni ₃ Co ₃ Al _0.5 0 ₂ , LiMn _3.5 Ni ₃ Co ₃ B _{0. 5} 0 ₂ , LiMn _3.5 Ni ₃ Co ₃ Fe _0.5 0 ₂ , LiMn _3.5 Ni ₃ Co ₃ Mg _0.5 0 _2, or the like can be used. In the composition, if Ni is increased, the capacity can be increased, if Co is increased, the output at a low temperature can be improved, and if Mn is increased, the material cost can be suppressed. Further, the additive element is effective in stabilizing the cycle characteristics, and also contributes to the improvement of safety when the amount of Ni is large. Among them, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ has high low temperature characteristics and high cycle stability and is suitable as a lithium battery material for HEV. Furthermore, it is preferable to mix conductive carbonaceous materials such as graphite, amorphous, activated carbon, etc. in order to constitute the electrode.

As the negative electrode material, natural graphite, composite carbonaceous material formed with a film formed by dry CVD (Chemical 1 Vapor Deposition) method or wet spray method on natural graphite, resin raw materials such as epoxy and phenol, or petroleum or coal A carbonaceous material such as artificial graphite or amorphous carbon material produced by firing from a pitch-based material obtained from the above, or lithium metal that can occlude and release lithium by forming a compound with lithium, lithium and a compound An oxide or nitride of a Group 4 element such as silicon, germanium, or tin that can be formed or inserted into a crystal gap to occlude and release lithium can be used. Among them, the carbonaceous material has high conductivity and is excellent in terms of low temperature characteristics and cycle stability. Among the carbonaceous materials, a material having a wide carbon network plane layer (d ₀₀₂ ) is excellent in rapid charge / discharge and low temperature characteristics, and is suitable as the material of the present invention. However, since a material having a wide carbon network interlayer d ₀₀₂ may have a reduced capacity and a low charge / discharge efficiency at the initial _stage of charging, d ₀₀₂ is an O.D. 39 nm or less is preferable. Furthermore, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like may be mixed to constitute the electrode.

  The high output type lithium secondary battery of the present invention has improved DCR at a low temperature as compared with the lithium secondary battery so far, and has improved input / output performance at a low temperature as compared with the conventional battery. The battery can be widely used as a power source for an electric control system or a backup power source, and is also suitable as a power source for industrial equipment such as electric tools and forklifts.

  In addition, the lithium secondary battery of the present invention has improved output characteristics particularly at low temperatures, and is effective for use in automobiles that are frequently used in cold regions. Further, when a battery is used as an assembled battery and actually used as a module of several hundred volts, since the low temperature characteristics are high, the number of necessary assembled batteries can be reduced, so that the module can be reduced in size and weight.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery which can improve a low temperature characteristic can be provided, without impairing the cycling characteristics of a lithium secondary battery.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to specific examples.

As an electrolytic solution, a solvent was mixed at the following volume composition ratio EC: DMC: EMC: MA = 3: 3: 3: 1, and LiPF ₆ was dissolved as a lithium salt to prepare an electrolytic solution.

Comparative Example 1

As a comparative electrolytic solution, a solvent mixed with the following volume composition ratio EC: DMC: DEC = 1: 1: 1 was used, and LiPF ₆ was dissolved as a lithium salt to prepare an electrolytic solution.
(Conductivity comparison)
FIG. 1 is a diagram showing the results obtained by comparing the conductivity of Example 1 and Comparative Example 1 with respect to the lithium salt concentration from the AC impedance of 3 kHz and comparing the results. As shown in FIG. 1, by changing the composition of the solvent constituting the electrolyte from DEC to a mixture of EMC and MA, the conductivity can be improved at each lithium salt concentration, and the highest conductivity can be achieved. You can see that the points are also higher.

FIG. 2 is a diagram showing the results of comparing the temperature dependence of the electrolyte solutions of Example 1 and Comparative Example 1 in which 1M LiPF ₆ was dissolved. The electrolytic solution of Example 1 maintained high conductivity as compared with the electrolytic solution of Comparative Example 1 up to a low temperature of −40 ° C. Thus, using EMC and MA together is effective in improving the conductivity of the electrolytic solution.

Next, LiMn _1/3 Ni _1/3 Co _1/3 0 ₂ is used as the positive electrode material, carbon black (CB1) and graphite material (GF1) are used as the conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. The solid content weight at the time of drying is as follows:
LiMn _1/3 Ni _1/3 Co _1/3 0 ₂ : CB1: GF1: PVDF = 86: 9: 2: 3
A positive electrode material paste was prepared using NMP (N-methylpyrrolidone) as a solvent. This positive electrode material paste is applied to the aluminum foil used as the positive electrode current collector 1, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode layer 2 on the positive electrode current collector 1. Formed.

Carbotron P made by Kureha Chemical is used as the negative electrode material, carbon black (CB2) is used as the conductive material, PVDF is used as the binder, and the solid content weight at the time of drying is as follows:
Carbotron P: CB1: PVDF = 88: 5: 7
A negative electrode material paste was prepared using NMP as a solvent. The negative electrode material paste is applied to the copper foil used as the negative electrode current collector 3, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the negative electrode layer 4 on the negative electrode current collector 3. Formed.

  FIG. 3 is a cross-sectional side view of the coin-type battery prepared in this example. The positive electrode and the negative electrode manufactured as described above are punched into a circle having a diameter of 15 mm, the polyethylene separator 7 having a thickness of 25 μm is sandwiched between them, and the electrolytic solution 1 of Example 1 is injected into the electrolytic solution. Then, the negative electrode was placed, the case 5 was covered, the gasket 8 was sandwiched, and the coin type battery (Example 1) having the structure shown in FIG.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: MA = 3: 3: 3: 1
The electrolyte solution was prepared by dissolving LIPF ₆ as a lithium salt to 1 M and mixing 0.8 wt% of VC.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: MA = 3: 3: 3: 1
LiPF ₆ as a lithium salt is dissolved so as to be 1 M, VC is 0.8% by weight, and the compound of formula 5 (tetrakis [trifluoroacetoxy] lithium borate; TTFBL) is 0 An electrolytic solution was prepared by mixing 0.01M.

Using the electrolytic solutions of Comparative Example 1, Example 2, and Example 3, coin-type batteries into which the electrolytic solution was injected were produced in the same manner as in Example 1.
(Evaluation of cell resistance)
FIG. 4 is a diagram showing the results of evaluating and comparing the direct current resistance (DCR) at −30 ° C. of the battery produced as described above. The produced battery was charged at a constant current of 2 mA, further charged at a constant voltage of 4.1 V until the current fell below 20 μA, and then discharged to 2.7 V at a constant current of 2 mA with a 30-minute shutdown. . After repeating this operation three times, the battery was further charged to 3.8 V at a constant current of 2 mA. In this state, discharge was performed at current values of 20 mA, 40 mA, and 60 mA to a final voltage of 2.5 V, the IV characteristics were measured, and the battery resistance at the time of discharge (output) was evaluated from the slope. In Example 2, it was found that the resistance on the electrode surface was increased by mixing VC. However, it was found that by adding TTFBL, the battery of Example 3 can suppress an increase in resistance at a low temperature due to VC. This seems to be because the bulky TTFBL anion reduces the density of the electrode coating. Thereby, the movement of lithium ions at a low temperature is improved, and the battery resistance is considered to be low.

  FIG. 5 is a half sectional view of the wound battery of the present example. The wound battery shown in FIG. 5 was produced, and the battery resistance at −30 ° C. and the pulse cycle characteristics were evaluated and compared. The battery was charged at a constant current of 0.7 A to 4.1 V, charged at a constant voltage of 4.1 V until the current value reached 20 mA, and after 30 minutes of operation stop, discharged at 0.7 A to 2.7 V. This operation was repeated three times. Next, the battery was charged with a constant current O.D. The battery was charged at 7 A, discharged at 10 A for 10 s, charged again at a constant current up to 3.8 V, discharged at 20 A for 10 s, charged again at 3.8 V, and discharged at 30 A for 10 s. The DCR of the battery was evaluated from the IV characteristics at this time. Moreover, the pulse cycle test which repeats charging / discharging of 20A-2s in the thermostat set to 50 degreeC was done, and the capacity | capacitance of 25 degreeC after 1000 h and DCR of 25 degreeC and -30 degreeC were evaluated.

  Table 1 shows the initial characteristics and the characteristics after the pulse cycle of Examples 1 to 3 and Comparative Example 1 in the wound battery shown in FIG. In the battery of Example 1 in which MA was mixed with the electrolytic solution, the initial DCR was reduced by 10-15% compared to the battery of Comparative Example 1 composed only of carbonate ester. That is, an improvement of 10-15% in input / output can be expected. In addition, the DCR increase rate after the pulse cycle was also suppressed by 1O-15% as compared with the battery of Comparative Example 1.

  Further, in the battery in which VC was mixed with the battery of Example 1, the initial DCR slightly increased as compared with the battery of Example 1, but the DCR increase after the pulse cycle was significantly suppressed. This is presumably because the electrode coating provided by VC suppresses the side reaction of the electrolyte in the pulse cycle.

  Furthermore, in the battery of Example 3 in which TTFBL was added to Example 2, the initial DCR was successfully reduced significantly at both 25 ° C. and −30 ° C. Furthermore, although the DCR after the pulse cycle was inferior in the rate of increase compared to Example 2, the absolute value was kept low and the cycle characteristics were good. As described above, it was confirmed that MA is effective in improving low temperature characteristics, VC contributes to improving cycle characteristics, and TTFBL is effective in greatly improving low temperature characteristics.

As an electrolytic solution, the following volume composition ratio is used: EC: DMC: EMC: EA = 3: 3: 3: 1
The electrolyte solution was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and mixing 0.8 wt% of VC, and injecting it into a battery having the same specifications as in Example 1. The battery of Example 4 was produced.

As an electrolytic solution, the following volume composition ratio is used: EC: DMC: EMC: EA = 3: 3: 3: 1
A battery having the same specifications as in Example 1 was prepared by dissolving LiPF ₆ as a lithium salt to 1 M, mixing 0.8 wt% of VC and 0.01 M of TTFBL. The battery of Example 5 was produced.

As an electrolytic solution, the following volume composition ratio of EC: DMC: EMC: PM = 3: 3: 3: 1
In this way, LiPF ₆ as a lithium salt is dissolved so as to be 1 M, and an electrolyte solution in which 0.8% by weight of VC is mixed is prepared, and poured into a battery having the same specifications as in Example 1. A battery of Example 6 was produced.

As an electrolytic solution, the following volume composition ratio is used: EC: DMC1EMC: PM = 3: 3: 3: 1
LiPF ₆ as a lithium salt was dissolved so as to be 1 M, VC was 0.8% by weight, and TTFBL was O.D. An electrolyte solution mixed with 01M was prepared and poured into a battery having the same specifications as in Example 1, and a battery of Example 7 was produced.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: PE = 3: 3: 3: 1
The electrolyte solution was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and mixing 0.8 wt% of VC, and injecting it into a battery having the same specifications as in Example 1. The battery of Example 8 was produced.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: PE = 3: 3: 3: 1
LiPF ₆ as a lithium salt was dissolved so as to be 1 M, VC was 0.8% by weight, and TTFBL was O.D. An electrolyte solution mixed with 01M was prepared, and poured into a battery having the same specifications as in Example 1, to produce a battery of Example 9.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: TFMA = 3: 3: 3: 1
The electrolyte solution was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and mixing 0.8 wt% of VC, and injecting it into a battery having the same specifications as in Example 1. The battery of Example 10 was produced.

As an electrolytic solution, the following volume composition ratio of EC: DMC = EMC: TFMA = 3: 3: 3: 1
LiPF ₆ as a lithium salt was dissolved so as to be 1 M, VC was 0.8% by weight, and TTFBL was O.D. An electrolyte solution mixed with 01M was prepared, and poured into a battery having the same specifications as in Example 1, to produce a battery of Example 11.
(Evaluation of battery characteristics of Examples 4 to 11)
Table 2 shows the results of tests and evaluations similar to the batteries of Examples 1 to 3 for Examples 4 to 11. The battery of Example 4 in which MA was replaced with EA had a DCR of 3 mΩ lower at 25 ° C. and 20 mΩ lower at −30 ° C. compared to Example 2. Further, the battery of Example 5 in which TTFBL was added to the electrolyte solution of Example 4 had a DCR of 3 mΩ lower at 25 ° C. and 30 mΩ lower at −30 ° C. than that of Example 4.

  The DCR of the battery of Example 6 in which MA was replaced with PM was 2 mΩ lower at 25 ° C. and 45 mΩ at −30 ° C. than that of Comparative Example 1. The battery of Example 7 in which TTFBL was added to the electrolyte solution of Example 6 had a DCR of 7 mΩ lower at 25 ° C. and 55 mΩ at −30 ° C. than that of Comparative Example 1.

  The DCR of the battery of Example 8 in which MA was replaced with PE was 3 mΩ lower at 25 ° C. than the battery of Comparative Example 1, and 40 mΩ lower at −30 ° C. Further, the battery of Example 9 in which TTFBL was added to the electrolyte solution of Example 8 had a DCR of 7 mΩ lower at 25 ° C. and 95 mΩ lower at −30 ° C. than the battery of Comparative Example 1.

  The DCR of the battery of Example 10 in which MA was replaced with TFMA was 2 mΩ lower at 25 ° C. and 30 mΩ at −30 ° C. than the battery of Comparative Example 1. Further, the battery of Example 11 in which TTFBL was added to the electrolytic solution of Example 10 had a DCR of 8 mΩ lower at 25 ° C. and 95 mΩ lower at −30 ° C. than that of Comparative Example 1. Even after the pulse cycle test, these example batteries maintained a low DCR at both 25 ° C. and −30 ° C. compared to the comparative example batteries.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: MA = 3: 3: 3: 1
In this way, LiPF ₆ as a lithium salt is dissolved so as to be 1 M, and an electrolytic solution in which 0-8 wt% of MVC is mixed is prepared and injected into a battery having the same specifications as in Example 1. The battery of Example 12 was produced.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: MA = 3: 3: 3: 1
LiPF ₆ as a lithium salt is dissolved to 1 M, 0.8 wt% of MVC is mixed, and TTFBL is mixed with O.D. An electrolyte solution mixed with 01M was prepared, and poured into a battery having the same specifications as in Example 1, to produce a battery of Example 13.

As an electrolytic solution, the following volume composition ratio of EC = DMC: EMC: MA: TFPC = 3 = 2: 3: 1: 1
The electrolyte solution was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and mixing 0.8 wt% of VC, and injecting it into a battery having the same specifications as in Example 1. The battery of Example 14 was produced.

As an electrolytic solution, the following volume composition ratio of EC: DMC: EMC: MA: TFPC = 3: 2: 3: 1: 1
A battery having the same specifications as in Example 1 was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and preparing an electrolyte solution containing 0.8 wt% VC and 0.01 M TTFBL. The battery of Example 15 was produced.

As an electrolytic solution, the following volume composition ratio of EC: DMC: EMC: MA: VEC = 3: 2.5: 3: 1: 0.5
In this case, LiPF ₆ as a lithium salt is dissolved to 1 M, and an electrolyte solution is prepared by mixing 0,8% by weight of VC. The solution is injected into a battery having the same specifications as in Example 1. The battery of Example 16 was made.

As an electrolytic solution, the following volume composition ratio of EC: DMC: EMC: MA: VEC = 3: 2.5: 3: 1: 0.5
LiPF6 as a lithium salt is dissolved so as to be 1 M, VC is mixed by 0.8 wt%, and TTFBL is mixed with O.D. An electrolyte solution mixed with 01M was prepared, and poured into a battery having the same specifications as in Example 1, to produce a battery of Example 17.

As an electrolytic solution, a solvent is used in the following volume composition ratio EC: DMC: EMC: MA: ClEC = 3: 2.5: 3: 1: 0.5
The electrolyte solution was prepared by dissolving LiPF ₆ as a lithium salt so as to be 1 M, and mixing 0.8 wt% of VC, and injecting it into a battery having the same specifications as in Example 1. The battery of Example 18 was produced.

As an electrolytic solution, the following volume composition ratio of EC: DMC = EMC: MA: ClEC = 3: 2.5: 3: 1: 0.5
LiPF6 as a lithium salt was dissolved so as to be 1 M, and an electrolyte solution was prepared by mixing 0.8 wt% of VC and 0.01 M of TTFBL. The battery of Example 19 was produced by pouring the liquid.
(Evaluation of battery characteristics of Examples 12 to 19)
Table 3 shows the results of tests and evaluations similar to the batteries of Examples 1 to 19 for Examples 12 to 19. The battery of Example 12 in which the electrolytic solution VC of Example 2 was changed to MVC had a DCR of 3 mΩ at 25 ° C. and 0 mΩ at −30 ° C. compared to the battery of Comparative Example 1. Furthermore, in the battery of Example 13 in which TTFBL was mixed with the electrolyte solution of Example 12, the DCR was 6 mΩ smaller at 25 ° C. and 105 mΩ at −30 ° C. than the battery of Comparative Example 1.

  In the battery of Example 14 in which TFPC was mixed with the electrolyte solution of Example 2, the DCR was 1 mΩ lower at 25 ° C. and 70 mΩ at −30 ° C. than the battery of Comparative Example 1. Further, in the battery of Example 15 in which TTFBL was mixed with the electrolytic solution of Example 14, the DCR was 3 mΩ at 25 ° C. and 95 mΩ at −30 ° C. smaller than that of Comparative Example 1.

  In the battery of Example 16 in which VEC was mixed with the electrolytic solution of Example 2, the DCR was 3 mΩ lower at 25 ° C. and 50 mΩ at −30 ° C. than the battery of Comparative Example 1. Furthermore, in the battery of Example 17 in which TTFBL was mixed with the electrolyte solution of Example 16, the DCR was 8 mΩ lower at 25 ° C. and 75 mΩ at −30 ° C. than the battery of Comparative Example 1.

  In the battery of Example 18 in which ClEC was mixed with the electrolyte solution of Example 2, the DCR was 2 mΩ lower at 25 ° C. and 45 mΩ at −30 ° C. than the battery of Comparative Example 1. Furthermore, in the battery of Example 19 in which TTFBL was mixed with the electrolyte solution of Example 18, the DCR was 7 mΩ smaller at 25 ° C. and 45 mΩ at −30 ° C. than the battery of Comparative Example 1. Even after the pulse cycle test, these example batteries maintained a low DCR at both 25 ° C. and −30 ° C. compared to the comparative example batteries.

以上、実施例１〜１９によれば、リチウムニ次電池のサイクル特性を損なうことなく、低温特性を向上させることができる。

As mentioned above, according to Examples 1-19, a low temperature characteristic can be improved, without impairing the cycling characteristic of a lithium secondary battery.

  Further, in this embodiment, as a high output type lithium secondary battery, DCR at a low temperature is improved as compared with the lithium secondary battery so far, and the input / output performance at a low temperature is improved as compared with the conventional battery, and the hybrid vehicle. It can be widely used as a power source for automobiles, an electric control system for automobiles and a backup power source, and is also suitable as a power source for industrial equipment such as electric tools and forklifts.

  Further, the lithium secondary battery of this example has improved output characteristics particularly at low temperatures, and is effective for use in automobiles that are frequently used in cold regions. When the battery is used as an assembled battery and actually used as a module of several hundred volts, since the low temperature characteristics are high, the number of necessary assembled batteries can be reduced, so that the module can be reduced in size and weight. .

It is a diagram which shows the relationship between the lithium salt concentration of the electrolyte solution in connection with this invention, and electrical conductivity. It is a diagram which shows the relationship between the temperature of the electrolyte solution in connection with this invention, and electrical conductivity. It is a half sectional view of a coin type battery concerning the present invention. It is a diagram which shows the relationship between direct current | flow resistance and time in the coin-type battery concerning this invention. It is a half sectional view of the wound battery according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector aluminum foil, 2 ... Positive electrode layer, 3 ... Negative electrode copper foil, 4 ... Negative electrode layer, 5 ... Negative electrode case (lid), 6 ... Positive electrode case, 7 ... Separator, 8 ... Gasket, 9 ... Negative electrode lead, 10 ... Positive electrode lead, 11 ... Positive electrode insulator, 12 ... Negative electrode insulator, 13 ... Negative electrode battery can, 14 ... Gasket, 15 ... Positive electrode battery lid.

Claims (6)

In a lithium secondary battery having a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an organic electrolyte in a container The organic electrolyte solution is
Cyclic carbonate solvent represented by (Formula 1)

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ represent any one of hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, and a fluorinated alkyl group, and R ₁ , R ₂ , R ₃ and R ₄ may be the same or different.
A chain carbonate solvent represented by (Formula 2) and

(In the formula, R ₅ and R ₆ represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₅ and R ₆ may be the same or different. good)
A chain ester solvent represented by Formula 3

(In the formula, R ₇ and R ₈ represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₇ and R ₈ are the same or different, respectively. Also good)
A lithium secondary battery comprising: The organic electrolyte solution according to claim 1,
A compound represented by (formula 4) and

(Wherein R ₉ and R ₁₀ represent hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or a fluorinated alkyl group, and R ₉ and R ₁₀ are the same or different. Also good)
Compound represented by Formula 5

A lithium secondary battery comprising at least one of the following. 3. The positive electrode according to claim 1, wherein the positive electrode is LiMn _X M1 _y M2 _Z 0 ₂ (wherein M1 is at least one selected from Co and Ni, and M2 is Co, Ni, A1, B, Fe, Mg, Cr). At least one selected from x + y + z = 1, 0.2 ≦ x ≦ O.6, 0.2 ≦ y ≦ O.4, 0.05 ≦ z ≦ O.4) A lithium secondary battery comprising:   4. The lithium secondary battery according to claim 1, wherein the negative electrode is made of at least one of a carbonaceous material, an oxide containing a group IV element, and a nitride containing a group IV element. 5. The compound according to claim 4, wherein the positive electrode is a compound represented by LiMn _1/3 Ni _1/3 Co _1/3 0 ₂ , and the negative electrode has a d ₀₀₂ of O.D. A lithium secondary battery comprising the carbonaceous material having a thickness of 39 nm or less. In any one of Claims 1-5, the cyclic carbonate solvent represented by said (Formula 1) is ethylene carbonate, the chain carbonate solvent represented by said (Formula 2) is dimethyl carbonate and ethyl methyl carbonate, said (formula 3. A lithium secondary battery, wherein the chain ester solvent represented by 3) is methyl acetate and the compound represented by (Formula 4) is vinylene carbonate.

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